Scientists from the University of Waterloo in Canada asked nine women and nine men, ages 18-30, to walk on treadmills.

Researchers monitored how much oxygen the subjects were taking in, along with their muscle oxygen extraction rates.

"These results indicated that the peripheral and pulmonary oxygen extraction dynamics were remarkably faster in women," the study said. "Thus, contrary to the hypothesis, V̇O2 dynamics measured at the mouth at the onset of submaximal treadmill walking were faster in women compared with men."